Printing ink

ABSTRACT

This invention relates to an ink-jet ink substantially free of water and volatile organic solvents comprising at least one monofunctional (meth)acrylate monomer, including phenoxyethyl acrylate; at least one monofunctional N-vinyl amide monomer, including N-vinyl caprolactam; at least one radical photoinitiator; and at least one coloring agent. The ink has a viscosity of less than 100 mPas at 25° C., and the molar ratio of the at least one monofunctional (meth)acrylate monomer to the at least one monofunctional N-vinyl amide monomer is from 1.0 to 6.0.

This invention concerns inks for use in ink-jet printers. In particular,this invention concerns inks for use in ink-jet printers that are curedusing ultraviolet radiation.

In ink-jet printing, minute droplets of black, white or coloured ink areejected in a controlled manner from one or more reservoirs or printingheads through narrow nozzles on to a substrate which is moving relativeto the reservoirs. The ejected ink forms an image on the substrate. Forhigh-speed printing, the inks must flow rapidly from the printing heads,and, to ensure that this happens, they must have in use a low viscosity,typically below 100 mPas at 25° C. although in most applications theviscosity should be below 50 mPas, and often below 25 mPas. Typically,when ejected through the nozzles, the ink has a viscosity of less than25 mPas, preferably 5-15 mPas and ideally 10.5 mPas at the jettingtemperature which is often elevated to about 40° C. (the ink might havea much higher viscosity at ambient temperature). The inks must also beresistant to drying or crusting in the reservoirs or nozzles. For thesereasons, ink-jet inks for application at or near ambient temperaturesare commonly formulated to contain a large proportion of a mobile liquidvehicle or solvent. In one common type of ink-jet ink this liquid iswater—see for example the paper by Henry R. Kang in the Journal ofImaging Science, 35(3), pp. 179-188 (1991). In those systems, greateffort must be made to ensure the inks do not dry in the head due towater evaporation. In another common type the liquid is a low-boilingsolvent or mixture of solvents—see, for example, EP 0 314 403 and EP 0424 714. Unfortunately, ink-jet inks that include a large proportion ofwater or solvent cannot be handled after printing until the inks havedried, either by evaporation of the solvent or its absorption into thesubstrate. This drying process is often slow and in many cases (forexample, when printing on to a heat-sensitive substrate such as paper)cannot be accelerated.

Another type of ink-jet ink contains unsaturated organic compounds,termed monomers, which polymerise by irradiation, commonly withultraviolet light, in the presence of a photoinitiator. This type of inkhas the advantage that it is not necessary to evaporate the liquid phaseto dry the print; instead the print is exposed to radiation to cure orharden it, a process which is more rapid than evaporation of solvent atmoderate temperatures. In such ink-jet inks it is necessary to usemonomers possessing a low viscosity.

However, ink-jet inks largely based on monomers suffer from significantdraw-backs compared to ink-jet inks containing solvent or moretraditional inks such as screen or flexographic systems, where thehigher viscosities allowed give greater formulation latitude. Thesetypes of ink can have significant amounts of the monomer contentreplaced with acrylate oligomers or inert thermoplastic resins whosehigher molecular weight leads to a reduction in the number of bonds thatmust be formed during the curing process. When each link is formed thebond length between the repeat units reduces leading to shrinkage of thecured film and unless this is controlled stress is imparted to thesubstrate. With plastic substrates this film shrinkage can lead tosevere embrittlement of the printed article and post print finishing,such as guillotining, becomes problematic.

Traditionally UV ink-jet inks are formulated with difunctional acrylatemonomers in order to achieve adequate cure speeds. Inks produced fromthese types of materials suffer badly from film shrinkage and consequentsubstrate embrittlement. Theoretically it should be possible to reduceshrinkage by use of wholly monofunctional acrylate or vinyl monomerbased systems, however this approach has generally been avoided due tovery low cure speeds associated with monofunctional monomers.

There is therefore a requirement in the art for inks which achieve abalance between cure speed and film shrinkage without compromising thelow viscosity of the ink-jet ink.

Accordingly, the present invention provides an ink-jet ink comprising atleast one monofunctional (meth)acrylate monomer; at least onemonofunctional N-vinyl amide monomer; at least one radicalphotoinitiator; and at least one colouring agent; wherein the ink has aviscosity of less than 100 mPas at 25° C., and wherein the molar ratioof the at least one monofunctional (meth)acrylate monomer to the atleast one monofunctional N-vinyl amide monomer is from 1.0 to 6.0.

The present invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 shows a graph of cure response against composition for threeink-jet inks of the present invention,

FIG. 2 shows a graph of cure response against composition for an ink-jetink of the present invention containing NVP and IBOA.

The ink-jet ink of the present invention dries primarily by curing, i.e.by the polymerisation of the monomers present, as discussed hereinabove,and hence is a curable ink. The ink does not, therefore, require thepresence of water or a volatile organic solvent to effect drying of theink, although the presence of such components may be tolerated.Preferably, however, the ink-jet ink of the present invention issubstantially free of water and volatile organic solvents.

As explained hereinabove incorporating significant amounts ofmonofunctional monomers in inks has traditionally led to very poor UVcure response and hence multifunctional monomers have had to be added toboost cure. It has now been found that, at certain ratios, combinationsof monofunctional (meth)acrylate monomers with an N-vinyl amide monomersprovide a surprising synergistic effect, namely higher cure speeds areobserved than for either of the component monomers when taken alone.This effect is particularly beneficial in ink-jet inks formulated withmonofunctional monomers allowing cure speeds which are similar or evenbetter than those observed with difunctional and even trifunctional(meth)acrylate monomer-based inks.

N-Vinyl amides are well-known monomers in the art and a detaileddescription is therefore not required. N-Vinyl amides have a vinyl groupattached to the nitrogen atom of an amide which may be furthersubstituted in an analogous manner to the (meth)acrylate monomers.

Preferred examples are N-vinyl caprolactam (NVC) and N-vinyl pyrrolidone(NVP):

The monofunctional (meth)acrylate monomers are also well known in theart and are preferably the esters of acrylic acid. Preferred examplesinclude:

The substituents of the monofunctional monomers are not limited otherthan by the constraints imposed by the use in an ink-jet ink, such asviscosity, stability, toxicity etc. The substituents are typicallyalkyl, cycloalkyl, aryl and combinations thereof, any of which may beinterrupted by heteroatoms. Non-limiting examples of substituentscommonly used in the art include C₁₋₁₈ alkyl, C₃₋₁₈ cycloalkyl, C₆₋₁₀aryl and combinations thereof, such as C₆₋₁₀ aryl- or C₃₋₁₈cycloalkyl-substituted C₁₋₁₈ alkyl, any of which may be interrupted by1-10 heteroatoms, such as oxygen or nitrogen, with nitrogen furthersubstituted by any of the above described substituents. The substituentsmay together also form a cyclic structure.

In a preferred embodiment, the monofunctional (meth)acrylate is a cyclicmonofunctional (meth)acrylate. That is, the radical covalently bonded tothe (meth)acrylate unit is cyclic. The cyclic radical may be saturatedor unsaturated, including aromatic. Preferred cyclic monofunctional(meth)acrylates are phenoxyethyl acrylate (PEA), cyclic TMP formalacrylate (CTFA), isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate(THFA) or mixtures thereof. Most preferably, the monofunctional(meth)acrylates present are exclusively cyclic, i.e. they are the solemonofunctional (meth)acrylate(s) present.

The total amount of the at least one monofunctional (meth)acrylatemonomer and the at least one monofunctional N-vinyl amide monomer incombination is preferably at least 60 wt %, more preferably at least 70wt % and most preferably at least 80 wt %, based on the total weight ofthe ink.

The molar ratio of the at least one monofunctional (meth)acrylatemonomer to the at least one monofunctional N-vinyl amide monomer is from1.0 to 6.0. The upper limit to this ratio is preferably 4.0 or less,more preferably 3.5 or less, more preferably 2.0 or less and mostpreferably 1.6 or less. The lower limit to this ratio is preferably 1.1or more, more preferably 1.2 or more, more preferably 1.3 or more andmost preferably 1.5 or more. A particularly preferred range is 1.25 to1.53.

Monofunctional acrylates and monofunctional N-vinyl amide, whencombined, offer significant improvements in cure response over thenon-combined monomers. All of the combinations tested exhibited aminimum in the dose of UV light required for cure when cure response wasplotted against monomer blend composition (further details are given inthe examples hereinbelow). The depth of these minima are dependent onthe individual cure speeds of the component monomers: the faster curingthe acrylate monomers when taken alone, the deeper the minimum in UVdose required.

Of those tested, many blends exhibited faster cure speeds than DPGDA (adifunctional acrylate) and in some cases speeds equivalent to TMPTA (atrifunctional acrylate). These optimised blends provide significantadvantages: high cure speeds can be achieved without compromising filmproperties such as flexibility, which is often sacrificed whenmultifunctional acrylates are employed.

It is possible to modify further the film properties of the ink-jet inksby inclusion of multifunctional monomers, oligomers or inert resins,such as thermoplastic acrylics. However, it should be noted that in thecase of oligomers and multifunctional monomers the flexibility may beadversely affected and also that some adjustments to stoichiometry maybe required to retain optimum cure speed.

Examples of the multifunctional acrylate monomers which may be includedin the ink-jet ink formulation include hexanediol diacrylate,trimethylolpropane triacrylate, pentaerythritol triacrylate,polyethyleneglycol diacrylate, for example, tetraethyleneglycoldiacrylate), dipropyleneglycol diacrylate, tri(propylene glycol)triacrylate, neopentylglycol diacrylate, bis(pentaerythritol)hexa-acrylate, and the acrylate esters of ethoxylated or propoxylatedglycols and polyols, for example, propoxylated neopentyl glycoldiacrylate, ethoxylated trimethylolpropane triacrylate, and mixturesthereof. Particularly preferred are difunctional acrylates with amolecular weight greater than 200.

In addition, suitable multifunctional acrylate monomers include estersof methacrylic acid (i.e. methacrylates), such as hexanedioldimethacrylate, trimethylolpropane trimethacrylate, triethyleneglycoldimethacrylate, diethyleneglycol dimethacrylate, ethyleneglycoldimethacrylate; 1,4-butanediol dimethacrylate.

Mixtures of (meth)acrylates may also be used.

In one embodiment the ink is substantially free of multifunctionalmonomer, meaning that only trace amounts will be present, for example asimpurities in the monofunctional material or as a component in acommercially available pigment dispersion. Where multifunctional monomeris included, the multifunctional monomer is present in an amount of nomore than 30 wt %, preferably no more than 25 wt %, more preferably nomore than 20 wt % and most preferably no more than 15 wt % based on thetotal weight of the ink. The multifunctional monomer which is limited inamount may be any multifunctional monomer which could be involved in thecuring reaction, such as a multifunctional (meth)acrylate monomer or amultifunctional vinyl ether.

In an embodiment the ink is substantially free of oligomeric andpolymeric material meaning that only trace amounts will be present.Where oligomeric or polymeric material is included, the oligomeric andpolymeric material is present in an amount of no more than 20 wt %, morepreferably no more than 10 wt %, most preferably no more than 5 wt %based on the total weight of the ink. Oligomeric and polymeric materials(e.g. acrylate oligomers and inert thermoplastic resins, respectively)are known in the art and typically have a molecular weight above 500,more preferably above 1000.

In addition to the monomers described above, the compositions include aphotoinitiator, which, under irradiation by, for example, ultravioletlight, initiates the polymerisation of the monomers. Preferred arephotoinitiators which produce free radicals on irradiation (free radicalphotoinitiators) such as, for example, benzophenone, 1-hydroxycyclohexylphenyl ketone, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one,benzil dimethylketal,bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide ormixtures thereof. Such photoinitiators are known and commerciallyavailable such as, for example, under the trade names Irgacure, Darocur(from Ciba) and Lucerin (from BASF).

Preferably the photoinitiator is present from 1 to 20% by weight,preferably from 4 to 10% by weight, of the ink.

The ink-jet ink of the present invention also includes a colouringagent, which may be either dissolved or dispersed in the liquid mediumof the ink. Preferably the colouring agent is a dispersible pigment, ofthe types known in the art and commercially available such as, forexample, under the trade-names Paliotol (available from BASF plc),Cinquasia, Irgalite (both available from Ciba Speciality Chemicals) andHostaperm (available from Clariant UK). The pigment may be of anydesired colour such as, for example, Pigment Yellow 13, Pigment Yellow83, Pigment Red 9, Pigment Red 184, Pigment Blue 15:3, Pigment Green 7,Pigment Violet 19, Pigment Black 7. Especially useful are black and thecolours required for trichromatic process printing. Mixtures of pigmentsmay be used.

The total proportion of pigment present is preferably from 0.5 to 15% byweight, more preferably from 1 to 5% by weight.

Although the ink of the present invention cures by a free radicalmechanism, the ink of the present invention may also be a so-called“hybrid” ink which cures by a radical and cationic mechanism. Theink-jet ink of the present invention, in one embodiment, thereforefurther comprises at least one cationically curable monomer, such as avinyl ether, and at least one cationic photoinitiator, such as aniodonium or sulfonium salt, e.g. diphenyliodonium fluoride andtriphenylsulfonium hexafluophosphate. Suitable cationic photoinitiatorsinclude the Union Carbide UVI-69-series, Deuteron UV 1240 and IJY2257,Ciba Irgacure 250 and CGI 552, IGM-C440, Rhodia 2047 and UV9380c.

Other components of types known in the art may be present in the ink toimprove the properties or performance. These components may be, forexample, surfactants, defoamers, dispersants, synergists for thephotoinitiator, stabilisers against deterioration by heat or light,reodorants, flow or slip aids, biocides and identifying tracers.

The present invention also provides a method of ink-jet printing usingthe above-described ink and a substrate having the cured ink thereon.Suitable substrates include styrene, PolyCarb (a polycarbonate),BannerPVC (a PVC) and VIVAK (a polyethylene terephthalate glycolmodified). The ink of the present invention is preferably cured byultraviolet irradiation and is suitable for application by ink-jetprinting. The present invention further provides an ink-jet inkcartridge containing the ink-jet ink as defined herein. The cartridgecomprises an ink container and an ink delivery port which is suitablefor connection with an ink-jet printer.

The ink-jet ink exhibits a desirable low viscosity (less than 100 mPas,preferably less than 50 mPas and most preferably less than 25 mPas at25° C.).

(Meth)acrylate is intended herein to have its standard meaning, i.e.acrylate and/or methacrylate. Mono and multifunctional are also intendedto have their standard meanings, i.e. one and two or more groups,respectively, which take part in the polymerisation reaction on curing.

The inks of the invention may be prepared by known methods such as, forexample, stirring with a high-speed water-cooled stirrer, or milling ona horizontal bead-mill.

EXAMPLES

The invention will now be described, by way of example, with referenceto the following example (parts given are by weight).

Example 1 Reference Example

Ink-jet ink formulations were prepared by varying the monomercomposition whilst holding all the other components constant, as set outin Table 1.

TABLE 1 Cyan formulation used for all cure response testing. ComponentPercentage in formula Colour concentrate 4.53 Monomer 81.86 UVstabilizer 0.8 Irgacure 184 1.88 Acyl phosphine oxide 8.01 Benzophenone2.82 Silicone wetting agent 0.1

A series of monomers were evaluated in the above formula and comparedfor cure speed. Inks were drawn down onto to 220 micron gloss PVC usinga 12 micron K bar applicator. The films were cured using a Svecia UVdrier fitted with two independently switchable 80 W/cm lamps. In eachcase the UV dose required to cure the ink film to a tack-free state wasmeasured.

The results are set out in Tables 2a and 2b which show samples curedwith two lamps on full power and samples cured on half power,respectively.

TABLE 2a Cure speeds of monomers in test formula. UV Dose required No.of lamps & Belt speed Monomer (mJ/cm²) Power setting (m/min) TMPTA 105 2× half power 30 CTFA 220 2 × half power 16 DPGDA 400 2 × half power >10IBOA 480 2 × half power 7 PEA >480 2 × half power <7

TABLE 2b Cure speeds of monomers in test formula. UV Dose required No.of lamps & Belt speed Monomer (mJ/cm²) Power setting (m/min) THFA 500 2× full power 14 EOEOEA 840 2 × full power 8 NVC 1000+ 2 × full power <7TDA 1000+ 2 × full power <7 ODA  1000++ 2 × full power <<7 IDA  1000++ 2× full power <<7 Lauryl acrylate  1000++ 2 × full power <<7

Example 2

Further studies on blends of monofunctional acrylate highlighted acuriosity, that a blend of monofunctional acrylate with NVC showed a nonlinear cure speed response, a maximum in the cure response beingobserved, for example, at a NVC:PEA ratio of 1:1.7 by weight. Table 3sets out the monomer compositions which provided the maximum cure speedfor each monomer pair.

TABLE 3 Monomer composition at peak cure response. UV dose for % Molarratio cure % NVC by monoacrylate Monoacrylate/ Monomer (mJ/cm²) weightby weight NVC THFA 205 30 51.86 1.53 IBOA 140 30 51.86 1.15 EOEOEA 70015 66.86 3.30 IDA 880 30 51.86 1.13 PEA 200 30 51.86 1.25 CTFA 120 37.544.36 1.47

The data from Tables 2 and 3 are summarised in Table 4:

TABLE 4 Minimum UV dose for individual acrylates and correspondingNVC/acrylate blends. UV dose for cure (mJ/cm²) Monomer Acrylate onlyAcrylate + NVC THFA 500 205 IBOA 480 140 EOEOEA 840 700 IDA  1000++ 880PEA >480  200 CTFA 220 100 TMPTA 105 <60 NVC 1000+ 1000+

FIG. 1 also shows a graphical representation of UV dose minima againstthe amount of NVC present. Where the amount of NVC is zero, the dosesfor cure are as set out in Reference Example 1. As the amount of NVC isincreased the dose required for cure decreases showing that the additionof NVC advantageously increases cure speed. The increase in cure speedprovides an improved ink with the maximum improvement in the cure speedbeing identified by the minima in FIG. 1. By way of a reference, thedoses required for the cure of the di- and trifunctional acrylates DPGDAand TMPTA when taken alone are also shown in FIG. 1.

Example 3

During the evaluation it was noted that combinations of NVC andN-acryloylmorpholine (ACMO) only did not exhibit this trend. Althoughnot wishing to be bound by theory, it is believed that this may be dueto the similar nature of the unsaturation in the monomers, both havingnitrogen close to the double bond.

Example 4

A formula containing a blend of NVP and IBOA was prepared and evaluatedas described hereinabove with similar results which are set out in FIG.2.

Example 5

Particularly preferred examples of ink-jet inks of the present inventionare set out in Table 5:

TABLE 5 Preferred blends of acrylate and amide Monomer blend Weightratio Comparative speed THFA/NVC 51.86/30 Faster than DPGDA IBOA/NVC51.86/30 Faster than DPGDA PEA/NVC 51.86/30 Faster than DPGDA CTFA/NVC  44.36/37.5 Equivalent to TMPTA IBOA/NVP 51.86/30 Equivalent to TMPTA

Example 6

A cyan ink-jet ink formulation of the present invention was prepared bycombining the following components:

-   Pigment Dispersion * 4.53-   N Vinyl caprolactam 30.70-   Phenoxyethyl acrylate 51.16-   Firstcure ST-1 0.8-   Irgacure 184 1.88-   Acyl phosphine oxide 8.01-   Benzophenone 2.82-   Byk 307 0.1    *Pigment Dispersion:-   SOLSPERSE 32000 10.00-   FIRSTCURE ST-1 1.00-   SARTOMERSR 9003 59.00 (propoxylated NPGDA—difunctional)-   IRGALITE BLUE GLVO 30.00

The invention claimed is:
 1. An ink-jet ink substantially free of waterand volatile organic solvents comprising at least one monofunctional(meth)acrylate monomer; at least one monofunctional N-vinyl amidemonomer, wherein said at least one monofunctional N-vinyl amide monomeris selected from the group consisting of N-vinyl caprolactam (NVC) andN-vinyl pyrrolidone (NVP); at least one radical photoinitiator; at leastone colouring agent; wherein the ink has a viscosity of less than 100mPas at 25° C., and wherein the molar ratio of the at least onemonofunctional (meth)acrylate monomer to the at least one monofunctionalN-vinyl amide monomer is from 1.1 to 2.0, and further wherein saidink-jet ink has a higher cure speed than a cure speed of an ink-jet inkwhich comprises only one of the at least one monofunctional(meth)acrylate monomer and the at least one monofunctional N-vinyl amidemonomer.
 2. An ink jet ink as claimed in claim 1, wherein the totalamount of the at least one monofunctional (meth)acrylate monomer and theat least one monofunctional N-vinyl amide monomer is at least 60 wt %,based on the total weight of the ink.
 3. An ink-jet ink as claimed inclaim 1, wherein the ink contains no more than 30 wt % ofmultifunctional monomers based on the total weight of the ink.
 4. Anink-jet ink as claimed in claim 1, wherein the ink contains at least onemultifunctional monomer and one or more of the multifunctional monomersis a multifunctional (meth)acrylate monomer.
 5. An ink-jet ink asclaimed in claim 1, wherein the at least one monofunctional(meth)acrylate is selected from the group consisting of phenoxyethylacrylate (PEA), cyclic TMP formal acrylate (CTFA), isobornyl acrylate(IBOA), tetrahydrofurfuryl acrylate (THFA), 2-(2-ethoxyethoxy}ethylacrylate, octa/decyl acrylate (ODA), tridecyl acrylate (TDA), isodecylacrylate (IDA) and lauryl acrylate.
 6. An ink-jet ink as claimed inclaim 1, wherein the at least one monofunctional (meth)acrylate isacyclic monofunctional (meth)acrylate.
 7. An ink-jet ink as claimed inclaim 1, wherein the molar ratio of the at least one monofunctional(meth)acrylate monomer to the at least one monofunctional N-vinyl amidemonomer is from 1.2 to 2.0.
 8. An ink-jet ink as claimed in claim 2,wherein the total amount is at least 70 wt %.
 9. An ink-jet ink asclaimed in claim 8, wherein the total amount is at least 80 wt %.
 10. Anink-jet ink as claimed in claim 5, wherein the ink contains acombination of monomers selected from the group consisting of THFAtetrahydrofurfuryl acrylate)/NVC (N-vinyl caprolactam), IBOA (isobornylacrylate)/NVC (N-vinyl caprolactam), PEA(phenoxyethylacrylate)/NVC(N-vinyl caprolactam), CTFA (cyclic TMP formalacrylate)/NVC(N-vinyl caprolactam), IBOA(isobornyl acrylate)/ACMO(N-acryloylmorpholine) and IBOA(isobornyl acrylate)/NVP(N-vinylpyrrolidone).
 11. An ink-jet ink as claimed in claim 6, wherein the inkcomprises at least one cyclic monofunctional (meth)acrylate as the solemonofunctional (meth)acrylate(s) present.
 12. An ink-jet ink as claimedin claim 6, wherein the ink contains a combination of monomers selectedfrom the group consisting of THFA (tetrahydrofurfuryl acrylate)/NVC(N-vinyl caprolactam), IBOA (isobornyl acrylate)/NVC (N-vinylcaprolactam), PEA(phenoxyethyl acrylate)/NVC(N-vinyl caprolactam), CTFA(cyclic TMP formal acrylate)/NVC(N-vinyl caprolactam) , IBOA(isobornylacrylate)/ACMO (N-acryloylmorpholine) and IBOA(isobornylacrylate)/NVP(N-vinyl pyrrolidone.
 13. An ink-jet ink as claimed inclaim 6, wherein the cyclic monofunctional (meth)acrylate isphenoxyethyl acrylate (PEA), cyclic TMP formal acrylate (CTFA),isobornyl acrylate (IBOA), tetrahydrofurfuryl acrylate (THFA), ormixtures thereof.
 14. An ink-jet ink as claimed in claim 11, wherein thecyclic monofunctional (meth)acrylate is phenoxyethyl acrylate (PEA),cyclic TMP formal acrylate (CTFA), isobornyl acrvlate (IBOA),tetrahydrofurfuryl acrylate (THFA), or mixtures thereof.
 15. An ink-jetink as claimed in claim 11, wherein the ink contains a combination ofmonomers selected from the group consisting of THFA (tetrahydrofurfulylacrylate)/NVC(N-vinyl caprolactam), IBOA (isobornyl acrylate)/NVC(N-vinyl caprolactam), PEA(phenoxyethyl acrylate)/NVC(N-vinylcaprolactam),CTFA (cyclic TMP formal acrylate)/NVC(N-vinyl caprolactam),IBOA(isobornyl acrylate)/ACMO (N-acryloylmorpholine) and IBOA(isobornylacrylate)/NVP(N-vinyl pyrrolidone).
 16. A method of ink-jet printing,comprising printing the ink-jet ink as claimed in claim 1 onto asubstrate and curing the ink.
 17. A substrate having the ink-jet ink asclaimed in claim 1 printed thereon.
 18. An ink-jet ink cartridgecontaining the ink-jet ink as claimed in claim 1.